The overall objectives and goals of this project are to: a) evaluate the use of a non-human primate as a bioassay model for estimating the bioavailability of supplemental dietary iron; b) to apply stable isotope tracer methodology to the determination of relative supplemental iron bioavailability; and c) to determine the effect of heat and pressure processing of the basal diet on the bioavailability of supplemental iron compounds to monkeys and humans by utilization of stable iron isotope tracer methodology. The proposed experiments will quantitate a stable isotope tracer of iron in animals and humans by mass spectrometry. This involves the formation and purification of volatile chelates followed by ion abundance measurements with a mass spectrometer. The relative bioavailability of stable isotope containing forms of iron will be compared to relative bioavailability estimates determined by animal hemoglobin depletion-repletion assays. Monkeys will be adapted to the hemoglobin depletion-repletion assay in an attempt to develop an accurate model for estimating human response. Supplemental dietary iron bioavailability from processed (heat and pressure) or unprocessed semi-purified diets will be compared with chicks, rats and monkey bioassay models. Subsequently, serum labelling and hemoglobin incorporation of 54Fe-enriched ferrous sulfate, hydrogen-reduced and electrolytic elemental irons from processed and unprocessed diets will be estimated in monkeys and humans. These comparisons will determine a) the suitability of non-human primates as accurate models for human dietary iron utilization studies; b) the suitability of iron stable isotope tracer methodology in human and animal iron bioavailability determinations; and c) the effect of heat and pressure processing of the diet on the human bioavailability of different food iron supplements.